Flotation recovery of molybdenite

ABSTRACT

A process for separating molybdenite from copper concentrates containing copper and iron sulfides, gangue materials and an organic collector comprising (1) conditioning the concentrate in aqueous suspension at a pH below about 7 with a soluble metal salt; (2) contacting the so treated concentrate with hydrogen peroxide at pH of about 4 to about 8; (3) subjecting the concentrate from (2) to a soluble iron cyanide and/or a solution of phosphorus pentasulfide in sodium hydroxide while maintaining the pH at no higher than about 8.5 whereby the molybdenite is floated and (4) recovering the enriched molybdenite float.

United States Patent [191 Shirley a a1.

[451 May'21, 1974 1 1 FLOTATION RECOVERY OF MOLYBDENITE [75] Inventors: Joseph Floyd Shirley, Tucson, Ariz.;

Edward Frank Caropreso, Hightstown, N.J.; George Lamar Fraser, Magna, Utah I [73] Assignees FMC Corporation, New York, NY.

[22] Filed: June 7, 1971 [21] Appl. No.: 150,773

[52] US. Cl. 209/167 3,313,412 4/1967 Bloom 209/167 3,220,551 11/1965 Moyer 209/167 3,372,924 4/1968 Corbett 209/167 3,539,002 11/1970 Last 209/167 X Primary ExaminerRobert Halper [5 7] ABSTRACT A process for separating molybdenite from copper. concentrates containing copper and iron sulfides,

gangue materials and an organic collector comprising 0 (l) conditioning the concentrate in aqueous suspension at a. pH below about 7 with a soluble metal salt;

(2) contacting the so treated concentrate with hydrogen peroxide at pH of about 4 to about 8;(3) subjecting the concentrate from (2) to a soluble iron cyanide and/or a solution of phosphorus pentasulfide in sodium hydroxide while maintaining the pH at no higher thanabout 8.5 whereby the molybdenite is floated and (4) recovering the enriched molybdenite float.

14 Claims, No Drawings FLOTATION RECOVERY OF MOLYBDENITE BACKGROUND OF THE INVENTION l. Field of the invention This invention relates to sulfide ores, particularly to the recovery of molybdenite from flotation concentrates containing a minor amount of molybdenite relative to other metal sulfides.

2. Description of the Prior Art The mineral molybdenite is a naturally occuring molybdenum sulfide (M08 and is the principal orefrom which metallic molybdenum is obtained. Molybdenite commonly occurs as a minor component in ores containing other metallic sulfides and is recovered therefrom as a by-product in the refining of copper ores by froth flotation. This is a widely used mining technique for the separation of minerals from their ores based on the differential wetting of the particles of finely ground ore.

In the recovery of molybdenite by froth flotation, it is common practice to start with mill concentrates or copper concentrates as they are more often called. These are partially refined sulfide ores from which much of the gangue material has been removed by froth flotation. Mill concentrates usually contain about l5 to about 30 percent copper while the molybdenite assay is typically of the order of 0.2 to 3 percent; other sulfides such as iron sulfide as well as some non-sulfide components may be present.

Since mineral separation by froth flotation depends on the difference in wetting properties of the mineral and ore particles, it is desirable to enhance such differential wetting by means of various collectors and/or depressant agents. Thus, where molybdenite is recovered from copper concentrates, the most common practice is to depress the associated copper and iron minerals while the molybdenite is floated off therefrom using a liquid hydrocarbon, for example, as a smearing collector for the molybdenite.

Accordingly, it is necessary to remove the previously added collectors from the copper and iron sulfide minerals in order to facilitate a separation. One approach to this problem has been the simple addition of a depressant to displace the organic collector from the copper and iron sulfide mineral surfaces. For instance, US. Pat. No. 2,492,936 to Nokes et al. discloses several reagents which can be used for this purpose. However, because rather large addition rates of these chemicals are required to obtain satisfactory results, the process is uneconomical where the molybdenite content is relatively low. In U.S. Pat. No. 2,664,l99 to Barker et al., sodium ferrocyanide is used to depress copper and iron sulfide minerals after previous conditioning with mild acid. Although this procedure has worked reasonably well in the treatment of chalocite concentrates, it is generally unsatisfactory when treating concentrates containing predominently chalcopyrite.

Another approach to separating molybdenite from copper concentrates has been to destroy or chemically alter the previously added copper collectors. This is accomplished in US. Pat. No. 2,255,776 to Janney et al. by various heat treatments. For instance, steaming is quite effective for removing xanthate type collectors from copper concentrates containing primarily chalcocite, but gives poor results with copperconcentrates containing predominently chalcopyrite. Moreover, the

concentrates due to the relatively high capital investment required. In US. Pat. No. 2,559, l 04 to Arbiter et al. it is suggested that by treating the copper concentrates with an oxidizing agent the copper collectors can be destroyed or altered toloose their collecting ability. As a result the copper and iron sulfide minerals are said to be depressed. Although reasonably successful with copper concentrates containing primarily chalcocite,

the procedure does not work satisfactorily on concentrates containing primarily chalcopyrite.

In a more recent patent, namely US. Pat. No. 3,137,649 to DeBenedictis et al., copper concentrates are subjected to oxidative treatment with hydrogen peroxide under rigidly controlled conditions of time and pH. The conditioned pulp is then given a froth flotation treatment in the presence of iron cyanide as a depressant. The process is effective in treating copper concentrates which have been collected .with a muthate type collectors, but it has failed to treat satisfactorily copper concentrates collected with a thiophosphate.

Although the aforedescribed processes exhibit varying degrees of efficiency, they have not proved to be entirely satisfactory for one reason or another. As a consequence, the art is still seeking further advances in the conditioning of copper concentrates for the purpose of effecting separation of molybdenite from accompanying sulfide ores.

SUMMARY OF THE INVENTION It has now been discovered that molybdenite can be separated from copper concentrates recovered by means of organic collectors and containing primarily copper and iron sulfide minerals as well as various gangue materials by (l) conditioning such concentrates with a soluble metal salt at a pH below about 7; (2) subjecting the so treated concentrates to a second conditioning with an oxidant; (3) subjecting the so conditioned concentrate to a depressant system which selectively depresses the molybdenite fraction and (4) subjecting the molybdenite to froth flotation to recover the enriched molybdenite float.

GENERAL DESCRIPTION In accordance with the invention, copper concentrate (usually containing O.252.0 percent molybdenite and about 25 percent copper or iron in the form of a mixed sulfide) may be treated as it comes from the copper concentration plant or it may be thickened to contain 40-60 percent solids. Treatment in the first conditioning step consists of adding fuel oil and a solution containing the dissolved metal salt. Acid is also added at this point for pH control or adjustment. The pulp is next treated in a second conditioning tank with an oxidant preferably hydrogen peroxide or another peroxygen compound and again adjustment of the pH with acid or base may be necessary. The pulp is next treated with a depressant or depressants before it enters the rougher flotation cells. Since the various depressants require different conditions for satisfactory operation, the pH of the pulp at this point will be dictated by the choice of depressant or depressants.

The copper concentrate may contain 16-60 percent solids although we prefer to work at 40-60 percent solids. Less reagents are required at the higher pulp densities and thus should be as high as possible in the interest of low operating costs.

The amount of fuel oil required to produce a hydrophobic surface on the molybdenite will depend on the ore. Usually 0.1-1.0 lb. of fuel oil per ton of concentrate is sufficient. It is preferred that the fuel oil be added prior to addition of oxidant.

Sufficient metal salt should be added to react with all or most of the collector which is contained in the copper concentrate. Normally, 0.5-3.0 lb. of metal salt per ton of concentrate is satisfactory. So far as we have been able to ascertain, any soluble metal salt capable of reacting or complexing with the dithiophosphate or the products of the reaction of the oxidant with the dithiophosphates can be used. However, it has been our experience that soluble metal sulfates particularly cupric sulfate, aluminum sulfate, and- /or zinc sulfate provides reproducible and highlysatisfactory results at low cost. l

During the first conditioning step, pH control is not particularly critical. However, it is desirable to adjust the pH to about 5.5-7.5 so as to provide suitable conditions for the oxidant reaction in the second conditioning step.

Temperature and time do not appear to be critical factors during the first conditioning operation.

Following the first conditioning operation the oxidant is added. The amount of oxidant is dependent on the ore, the type of oxidant, the slurry density, the type and amount of dithiophosphate used as collectors and the particular depressant or depressants used in the subsequent rougher flotation circuit. So far as we have been able to ascertain, any number of oxidants are suitable although we prefer peroxygen compounds such as monosulfate, alkali metal peroxides or hydrogen peroxide, the latter being especially preferred.

Broadly, we have found that the process disclosed in the invention can be carried out using about 0.25 to about 4 lbs. of hydrogen peroxide per ton of concentrate, althoughthe preferred range is about 0.5-2 lbs. per ton of concentrate. The reaction between the dithiophosphate, metal ion and hydrogen peroxide occurs rather rapidly between a pH of about 4 and 8 whereas outside this range the reaction procedes more slowly. Optimum pH range is in the vicinity of 5.5-7.5.

After the hydrogen peroxide addition, the pH of the pulp is adjusted to provide proper conditions in the rougher flotation cells. Thus, in order that the ferrocyanide function satisfactorily as a depressant, the pH should be between 6.5 and 8.5 and therefore the pulp pH should be less than 8.0. The reason for operating below pH 8 is that ferrocyanide reacts with excess H and converts a portion of the ferrocyanide to ferricyanide. This reaction results in an increase in pH. Thereammonium and alkali metal persulfates, sodium perfore, to achieve the requisite condition in the rougher circuit the pulp should be below pH of 8.0.

One of the particularly desirable aspects of the present process is that it effects separation of molybdenite from most iron and copper sulfide minerals including the difficult pyrite and chalcopyrite types and, of course, as well as the more easily treated chalcocite ores. Moreover, the process is effective in removing dithiophosphate collectors which are stable and difficult to destroy. It is to be pointed out that if, copper sulfate is the metal salt chosen the copper sulfate and part of the acid used in the first conditioning step can come from copper leach solutions which are available at most mills. Thus, the copper values from these leach solutions can be recovered easily and economically since the copper in the process eventually ends up in the smelter in any event. Normally, the copper in leach solutions is recovered by precipitation, so the present process effects its precipitation using chemicals already in the circuit. Where sulfide type depressants e.g. sodium sulfide, (Na S) sodium hydrosulfide (NaHS) are used in the molybdenite recovery circuit, their requirement will be greatly reduced from what it would be if the copper concentrates were not pre-conditioned with copper sulfate and hydrogen peroxide in accordance with the invention.

Reference is now made to the following non-limiting examples.

Experimental. Procedure MATERIALS The copper concentrates consisted primarily of chalcoprite and pyrite with minor amounts of chalcocite, bornite, molybdenite and tale. The major collector used to promote the copper minerals in these concentrates was either a mixture of P 8 and cresylic acid or Aerofloat 238, a product of American Cyanamid reported to be sodium di-secondary butyl dithiophosphate. Two batches of concentrates were processed having the following assay:

Series A 1.56% MoS 27.3% Cu Series B 2.85% MoS 32.3% Cu REACTION CONDITIONS A. 8-15 minutes with the indicated quantity of metal sulfate, and 0.033 lb/ton of fuel oil at a pH of 6.5.

B. Treatment for 5 minutes with hydrogen peroxide at pH 6.5.

C. Sodium ferrocyanide and/or a Nokes reagent (13 parts NaOH to 10 parts P 5 were then added as depressants. When used in combination, the sodium ferrocyanide was added first and allowed to mix for 1 min ute before addition of the Nokes reagent. Approximately 0.165 lb/ton of methyl amyl alcohol frother was also added.

D. The conditioned pulp was floated for 6 minutes at a final pH ranging from 7.7 8.0. The molybdenite was then separated as an enriched float in the rougher.

The individual examples are summarized in the Table below.

Conditioning agents Concentrate Tailing Depressant system Metal sulfate Percent Assay percent Distribution Assay percent Distribution Example H202. I lIh tSs/NiiOH. t. No. Name lb/ton lb/ton lbs/ton lbs/ton floated M082 Cu MoSt Cu M082 Cu MoS- Cu 1A 0.8 1.25 91.32 Essentially no M052 separation 2A 1. .8 89.75 Essentially no MoS2 separation 3A... 1. 1.25 88.10 Essentially no M separation 4A... 1. 8 1.25 88.72 Essentially no MOS; separation 5A... CUSOt-SlhO... 2.0 1.0 85.95 1.64 28.2 94.2 93.2 0.62 12.7 5.9 6.8 6A... CuSOt5H2O... 2.0 1.0 1.6 73.19 2.06 29.6 96.2 81.5 .22 18.4 3.8 18.5 7A... CuSO4-5H2O... 2.0 1.0 1.25 24.29 6.35 27.1 94.4 25.0 .12 26.1 5.6 75.0 8A... .CuS045H O... 2.0 1.0 0.8 1.0 19.60 7.3 27.1 20.6 .22 25.4 11.0 79.4 9A... 211504-71'120... 3.2 1.0 .8 1.25 14.80 9.4 25.6 90 1 14.5 .18 26.3 9.9 85.5 10A A 2(SO-|)L\--- 4.0 1.0 .8 1.25 13.70 9.7 27.0 84.6 14.0 .28 26:4 15.4 86.0 1B ZnSO4'7H2 3.2 0.5 .8 0.94 11.50 14.2 28.6 73.6 10.4 .66 31.9 26.4 89.6 213 ZnSO4'7H 3.2 .7 .8 1.15 12.80 12.6 25.1 81.5 11.0 .42 29.6 18.5 89.1 3B... ZnSOt'7H O 3.2 1.0 .8 1.15 5.90 33.2 17.0 91.3 3.2 .20 32.6 8.7 96.8 4B... ZnSOr7l-l2On 3.2 1.0 .8 0.94 12.05 15.0 25.3 63.9 9.9 1.16 31.7 36.1 90.1 513... ZnSO.-7H2O.. 3.2 1.0 .8 1.25 6.20 37.5 13.3 87.9 2.6 0.34 32.7 12.1 97.4 68 ZnSO4'7H O 3.2 .8 1.25 6.80 21.7 22.8 60.7 4.9 1.02 32.2 39.3 95.1

' Lbs/ton values based on P255 added.

Analysis of Test Data 4. sub ecting the molybdenite to froth flotation to recover the enriched molybdenite float.

The data summarized in the Table show:

1. The necessity for conditioning with both a metal sulfate and H 0 before flotation. This was demonstrated by the observation that the following reagent schedules were ineffective for separating M05 from copper concentrates promoted with dithiophosphate type collectors.

c. H O Na Fe(CN)tt P s /NaOH d. CuSO Na Fe(CN),, P S /NaOH 2. That several depressant systems are applicable, e.g. sodium ferrocyanide, Nokes reagent (mixture of P S /NaOH), and mixtures of the two. Best results with respect to physical characteristics and metallurgical analysis were obtained using the combination of reagents.

3. That metal sulfates such as CuSO ZnSO and Al (SO may be used. When using the combination depressant system Na Fe(CN) and P S /NaOH, the ZnSO gave the better results.

4. The dependence of MoS separation upon H 0 usage metallurgical results improved with increasing quantities of H 0 5. At constant sodium ferrocyanide usage, improved metallurgical results are obtained by using increasing amounts of the P S =,/NaOl-l mixture.

What is claimed is:

1. In a process for the separation of molybdenite from copper concentrates obtained by froth flotation in the presence of an organic collector, the improvement whereby the molybdenite is recovered in a more concentrated form comprising:

1. conditioning the concentrate in aqueous suspension at a pH below about 7 with a water soluble metal salt of copper, zinc or aluminum;

2. contacting the so-treated concentrate with an oxidant selected from the group consisting of hydrogen peroxide, sodium peroxide, ammonium, alkali metal persulfate and sodium permonosulfate;

3. subjecting the so conditioned concentrate to a depressant selected from the group consisting of sodium or potassium ferricyanide, sodium or potassium ferricyanide,-Nokes reagent (mixture of P s and NaOH), sodium sulfide and sodium hydrosulfide or mixtures thereof which selectively depresses the non-molybdenite fraction and 2. A process according to claim I wherein the organic collector used to produce said copper concentrates is selected from the group consisting of a dithiophosphate, a xanthate and a carbamate or mixtures thereof.

3. A process according to claim 1 wherein the soluble metal salt is selected from the group consisting of a copper sulfate salt, a zinc sulfate salt and an aluminum sulfate salt or mixtures for a 4. A process according to claim 1 wherein the principal collector used to produce the copper concentrate is a dithiophosphate; the concentrate is thickened to l660 percent solids and treated for period of time with a soluble metal of copper, zinc and aluminum and fuel oil; the pulp treated with a peroxygen compound defined in claim 4 at a pH of 4-8; the thus conditioned pulp subjected to froth flotation using a depressant or depressants as defined in claim 5 and recovering molybdenite from the enriched float.

5. A process according to claim 4 wherein the concentrate is thickened to 40-60 percent solids and treated for l-20 minutes with a soluble metal salt before the addition of the peroxygen compound.

6. A process according to claim 4 wherein 0.5 3.0 lbs of a metal salt per ton of concentrate is added.

7. A process according to claim 6 wherein the soluble metal salt is selected from the group consisting of cupric sulfate, zinc sulfate and aluminum sulfate.

8. A process according to claim 7, wherein the source of the metal salt is a leach solution containing the metal sulfate.

9. A process according to claim 4 wherein 0.254.0 pounds of H 0 per ton of concentrate is added.

10. A process according to claim 4 wherein the depressant is ferrocyanide and/or a mixture of ferrocyanide and ferricyanide.

11. A process according to claim 4 wherein the depressant is Nokes reagent (a mixture of P S /NaOH).

12. A process according to claim 4 wherein depressant is Na S and/or NaSH.

13. A process according to claim 4 wherein the depressant is a mixture of ferrocyanide and Nokes reagent (P S /NaOl-l).

14. A process according to claim 4 wherein the collector used to produce the copper concentrate is a dithiophosphate of the type obtained by reacting cresylic acid and P285.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3 Patent No. 3 811,569 Dated May 21, 1974 Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Inventor's name, page 1, "Edward Frank Caropreso" should read -Frank Edward Caropreso--.

Column 6, claim 3, line 29, "for a" should read '--thereof--;

Column 6, claim 4, change claim nos. to read 'claim 2-- both occurrences.

Column 2, line 50, "the molybdenite fraction" should read '--the non-molybdenite fraction--. (Applicants' error) Signed and sealed this I 7th day of June 1975.

(SEAL) Attest:

' C. IMRSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks FORM PO- (10-69) uscoMM-DC scam-Pe U.S. GOVERNMENT PRINTING OFFICE: 8 69- 9 O 

2. contacting the so-treated concentrate with an oxidant selected from the group consisting of hydrogen peroxide, sodium peroxide, ammonium, alkali metal persulfate and sodium permonosulfate;
 2. A process according to claim 1 wherein the organic collector used to produce said copper concentrates is selected from the group consisting of a dithiophosphate, a xanthate and a carbamate or mixtures thereof.
 3. A process according to claim 1 wherein the soluble metal salt is selected from the group consisting of a copper sulfate salt, a zinc sulfate salt and an aluminum sulfate salt or mixtures for a
 3. subjecting the so conditioned concentrate to a depressant selected from the group consisting of sodium or potassium ferricyanide, sodium or potassium ferricyanide, Nokes reagent (mixture of P2S5 and NaOH), sodium sulfide and sodium hydrosulfide or mixtures thereof which selectively depresses the non-molybdenite fraction and
 4. A process according to claim 1 wherein the principal collector used to produce the copper concentrate is a dithiophosphate; the concentrate is thickened to 16-60 percent solids and treated for period of time with a soluble metal of copper, zinc and aluminum and fuel oil; the pulp treated with a peroxygen compound defined in claim 4 at a pH of 4-8; the thus conditioned pulp subjected to froth flotation using a depressant or depressants as defined in claim 5 and recovering molybdenite from the enriched float.
 4. subjecting the molybdenite to froth flotation to recover the enriched molybdenite float.
 5. A process according to claim 4 wherein the concentrate is thickened to 40-60 percent solids and treated for 1-20 minutes with a soluble metal salt before the addition of the peroxygen compound.
 6. A process according to claim 4 wherein 0.5 - 3.0 lbs of a metal salt per ton of concentrate is added.
 7. A process according to claim 6 wherein the soluble metal salt is selected from the group consisting of cupric sulfate, zinc sulfate and aluminum sulfate.
 8. A process according to claim 7, wherein the source of the metal salt is a leach solution containing the metal sulfate.
 9. A process according to claim 4 wherein 0.25-4.0 pounds of H2O2 per ton of concentrate is added.
 10. A process according to claim 4 wherein the depressant is ferrocyanide and/or a mixture of ferrocyanide and ferricyanide.
 11. A process according to claim 4 wherein the depressant is Nokes reagent (a mixture of P2S5/NaOH).
 12. A process according to claim 4 wherein depressant is Na2S and/or NaSH.
 13. A process according to claim 4 wherein the depressant is a mixture of ferrocyanide and Nokes reagent (P2S5/NaOH).
 14. A process according to claim 4 wherein the collector used to produce the copper concentrate is a dithiophosphate of the type obtained by reacting cresylic acid and P2S5. 